When a patient is incised for surgery, the sides of the incision are parted and are held apart by a retractor so that the surgeon has the required access to the patient's body. Conventionally, previously proposed retractors for chest surgery comprise two parallel arms, with blades disposed thereon to engage the sternum (breastbone). The operation of these retractors is such that the retractor arms remain parallel throughout their range of motion, resulting in the sides of the incision being parted by the same amount along the length of the retractor.
With particular regard to cardiac (heart) surgery, the ribs attached to the lower (inferior) portion of the sternum are longer and are provided with more cartilage and greater elasticity than the ribs attached to the upper portion of the sternum. This results in the upper (superior) ribs having less tolerance for displacement. The use of parallel-opening retractors for spreading the sternum for cardiac operations exerts greater force on the upper ribs, which may fracture. Another disadvantage of these retractors is that their use in spreading the sternum may result in excessive traction on the nerves (brachial plexus) leading to the patient's arm. Damage to these nerves can cause weakness or long term loss of feeling in the patient's ring and little fingers. One way to avoid applying excessive stress to the upper ribs is to position the retractor as low as possible. However, this approach does not allow the retractor to be placed in the most advantageous position for chest surgery and can cause damage to the sternum by having mainly the edges, rather than the full surfaces, of the blades exerting pressure on the sides of the incision.
During surgery, it is often necessary to open the incision both horizontally and vertically. Typically, two separate retractors have been required for this, one for the horizontal opening and another for the vertical opening. The applicant has determined that it would be beneficial to have a single retractor which could part the sternum with minimal displacement at the upper end and maximal displacement at the lower end, a “V”-shaped displacement, in both the horizontal and vertical planes.